JackE said:

Yep. Under the old Windows naming convention, we're now way past Win11. Probably up to about Win21 with major updates coming about every 6mos ever since the first Win10 version debuted in 2014.

With that said, the old 5755g should be able to handle Win21, also known as Win10 version 21H1  though maybe a bit slowly.  Despite what you saw somewhere, uour BIOS chip hardware cannot magically be converted to the inherent security features of the UEFI chip hardware with a v1.21 firmware upgrade. To be frank, most folks really don't need the UEFI level of security anyway even though they think they do.

If it were mine,  I'd buy a new 2.5" 1TB WesternDigital Blue HDD for less than $50 from Amazon with free shipping. Then remove my old HDD and put it aside for safe-keeping. Put in the new WD10SPZX HDD. Then install Win21 on it with a USB stick using Microsoft's USB media creation tool   Then see how I like Win21.on my old relic.

If I like Win21, I'd then hook up m old HDD to a USB port with a 2.5" USB to HDD adapter for  less than $10 also from Amazon with free shipping on the same order. So I could copy all my personal files and favorite apps off the old drive on to the new one. If I don't like it, then I'd just put the old drive back in my old relic if I wanted to stay with Win7 or Win8x. Or do something better with the new HDD in my old relic.

In my case, I did something else much better with my old relic. It's even older than yours. I'm in fact using it right now in this response. But the 5755g  your machine. So you have to decide what to do. 

Hmm What's a relic to some is still serviceable to others ie a relic ford zetec engine can happily motor on past 200000 miles but a modern eco boost is not worth a fart in a working man's pants! . This acer 5755g is running the latest win10 quite speedily ssd installed and 8 gig of ram.  The question was can it run win11? I think you answered that which is appreciated. Now onto amazon I have not shopped via this company for at least 8 years and that will continue btw it's nothing they've done to me or price related. You can shop around the net and find great deals everydayif only peoplecould spare the time to do so. Cheers